15 Nucleus N o 64, 2018 XPS of carbon nanostructures obtained by underwater arc dis- charge of graphite electrodes Daniel Codorniu Pujals 1 , Dairon Rodríguez Garcés 2 , Olimpia Arias de Fuentes 2 , Luis F. Desdín García 3 1 Instituto Superior de Tecnologías y Ciencias Aplicadas (InSTEC), Universidad de La Habana, Cuba. 2 Instituto de Ciencia y Tecnología de Materiales (IMRE), Universidad de La Habana, Cuba. 3 Centro de Aplicaciones Tecnológicas y Desarrollo Nuclear (CEADEN), La Habana, Cuba. dcodorniu@instec.cu; codorniudp@gmail.com Abstract Carbon nanostructures, obtained by underwater arc discharge of graphite electrodes, were studied by X-Ray Photoelectron Spectroscopy (XPS). It was observed that the spectra of the samples taken from the foating part of the synthesis products, composed basically by Carbon nano-onions (CNO), present differences with those obtained from the precipitate, which contains a mixture of CNOs and multi-walled Carbon Nanotubes (MWCNT). These differences are related with the presence of atoms of carbon located in orbitals with different degree of hybridization (sp 2 -sp 3 ), which in turn is related to the diverse grade of curvature of the planes of carbon in the nanostructures present in the samples. The obtained results indicate that XPS can be an important element in the characterization of the products obtained by the above-mentioned method of synthesis. Key words: X-ray photoelectron spectroscopy; carbon nanotubes; graphite; raman spectroscopy; synthesis; transmission electron microscopy. XPS de nanoestructuras de carbono obtenidas por descarga de arco de electrodos de grafto sumergidos en agua Resumen Se utilizó la Espectroscopia Fotoelectrónica de Rayos X (XPS) para estudiar nanoestructuras de car- bono obtenidas por descarga de arco de electrodos de grafto sumergidos en agua. Se observó que los espectros de las muestras tomadas de la fracción fotante de los productos de la síntesis, compuestas básicamente por nano-cebollas de carbono (CNO), presentan diferencias con los de las muestras obtenidas del precipitado, que contiene una mezcla de CNOs y nano-tubos de carbono de capas múltiples (MWCNT). Estas diferencias están asociadas con la presencia de átomos de carbono localizados en orbitales con diferente grado de hibridación (sp 2 -sp 3 ), lo que a su vez se relaciona con las diferentes curvaturas de los planos de carbono en las nanoestructuras presentes en la muestras. Los resultados obtenidos indican que XPS puede ser un elemento importante en la caracterización de los productos obtenidos por el citado método de síntesis. Palabras clave: espectroscopía fotoelectrón de rayos X; nanotubos de carbono; grafto; espectroscopia raman; síntesis; mi- croscopía electrónica por transmisión. Introduction Carbon nanostructures, such as graphene, nano- tubes, nano-onions, nano-diamonds, and other, are being studied intensely by the scientifc community, due to their current and potential applications in Elec- tronics, Healthcare, Environmental Protection, Industry and many other felds. Their peculiar physical properties are also of special interest [1,2]. One of the most popular and simple method for ob- taining carbon nanostructures, especially nano-onions and nano-tubes, is the synthesis by underwater arc discharge of graphite electrodes, described by Sano in 2002 [3]. Since then, several authors have been using this technique to synthetize carbon nano-onions [4]. Due to the fact that the morphology and some physical properties of the nanostructures depend of the synthesis method used, it is very important to stu- dy in detail the characteristics of the nanomaterials obtained by underwater arc discharge. For example, recent studies by Transmission Electron Microscopy (TEM) and Raman Spectroscopy shown that an im- portant fraction of the nano-onions obtained by this technique has polyhedral structure [5,6], instead of the common spherical one obtained by other methods of synthesis [7, 8].